中文摘要：

DNA基因启动子甲基化是重要的表观遗传学机制之一，是导致抑癌基因表达沉默的重要分子生物学基础。乳腺癌患者外周血中循环游离DNA含量明显高于健康人，且具有与肿瘤原发灶一致的基因异常改变。研究显示，乳腺癌患者外周血循环游离DNA中存在多种基因甲基化异常，且与患者的临床病理特征存在不同程度的相关性，在乳腺癌的早期诊断、预后判断、疗效预测和复发监测等方面具有重要价值，本文就循环游离DNA甲基化在乳腺癌中的相关研究进展作一综述。

英文摘要：

DNA methylation is one of the most important epigenetic mechanism and molecular biological basis in tumor suppres- sor gene silencing. It is now well recognized that solid malignant tumors can release a significant amount of gcnomic DNA into sys- temic circulation, and with more than 90% of this total circulating cell-free DNA derived from tumor tissue, which can reflect the overall cell heterogeneity of the tumor itself. In breast cancer, the presence of abnormally high DNA concentrations in plasma has been reported, and changes in the levels of these circulating DNA associated with tumor burden and progression have been confirmed repeatedly. Accumulating data strongly suggested that DNA methylation patterns found in circulating cell free DNA were similarly with the primary tumor, and could be a useful biomarker in early diagnosis, prognosis assessment, and recurrence monitoring for breast cancer patients. Here, we summarize the latest advances in this research field.